The present invention relates generally to ophthalmic characterization, and more particularly to mapping retinal parameters from combined fundus image and three-dimensional optical coherence tomography.
Diagnostics for eye disorders typically include a detailed ophthalmic examination of the retina. For initial examination, an eye doctor will view the retina through an ophthalmoscope. For a permanent record, the retina is typically photographed with a fundus camera. A fundus photograph directly records various anatomical features of the retina, such as the optic disc, fovea, blood vessels, and lesions. The imaging capabilities of fundus photography may be enhanced by supplementary techniques. A high-contrast image of retinal blood vessels, for example, may be photographed after the injection of a fluorescent dye into the bloodstream. The resulting image is referred to as a fluorescein angiogram (FA).
More sophisticated techniques have recently been developed for diagnostics of the eye. One such technique is three-dimensional optical coherence tomography (3-D OCT). In this technique, a light beam is directed onto the retina. Part of the beam is back-reflected. Interferometric analysis of the back-reflected light yields information on the structure of the retina. By varying optical parameters of the light probe, features at different depths below the surface of the retina may be probed. With this process, an image of a cross-section of the retina may be generated by scanning the optical probe along a line on the retina. By rastering the optical probe across the surface of the retina, a series of cross-sectional images may be produced. The series of cross-sectional images may be used to characterize the 3-D structure of the retina, and parameters such as local retinal thickness may be measured by 3-D OCT.
The retinal thickness is dependent on the loci (points on the retina) at which the measurements are made. Of particular interest for diagnostics of the eye are variations of retinal thickness in a region about an anatomical feature. Some analytical instruments may provide a table of numerical values of retinal thickness as a function of position (specified by coordinates) on a retina. Other analytical instruments may map numerical values of retinal thickness to a grid covering the field of the retinal plane. Correlating numerical values of retinal thickness, either in tabular or grid format, with anatomical features is a difficult and, at best, a static process. What are needed are method and apparatus for a user, such as an ophthalmologist, to view a graphical representation of retinal thickness, or other parameter characterizing the retina, simultaneously with an image of anatomical structures in the retina. Method and apparatus which allow a user to view a graphical representation of a first parameter characterizing the retina mapped to a second parameter characterizing the retina are further advantageous.